In the sandboxed world of iOS development sharing data between applications can prove difficult. There are a number of reasons you may want your application to share data with other applications:

Releasing a paid app upgrade with a new SKU.

Moving user data to a universal binary.

Releasing a suite of complementary applications.

Partnerships with other developers.

Since iOS developers can’t share data directly through the file system [Did they ever plug this hole? -ed.], they need to find alternate solutions for their applications. Some common solutions include: